When an object is released from Windchill PDMLink, Windchill ESI services create one or more transaction objects, each of which represents the release of the object to a given ERP instance. Initially, each transaction object in the release has a status of pending; this indicates that the object data is being published to the Windchill ESI business logic. Windchill ESI services then query Windchill PDMLink for the object data and generate a formatted output that constitutes the Windchill ESI response for the given MES instance. The output is then sent to MES interface via delivery channel. For more information, see the Implementing Windchill ESI. Just before sending the message to MES interface the Windchill ESI services create a ReleaseActivity object for each Windchill PDMLink object and distribution target combination. The initial status of the Release Activity object is pending, indicating that the object/target has been published to the MES interface, but its outcome on the MES-side is not known. The existence of the pending ReleaseActivity object prevents the Windchill ESI services from publishing the object to the same distribution target again. After the MES interface processes each subtransaction (object/ target), it generates a completion notification. This notification includes the status (success or failure) and an optional textual message describing the status. When Windchill ESI services receive this notification, the services update the ReleaseActivity object for that specific object/target. Once Windchill ESI services receive the first completion notification for a subtransaction, they update the status of the relevant transaction the subtransaction is a part of to processing. At the end of processing the transaction, the MES interface generates a completion notification for the transaction. When Windchill ESI services receive this notification, they update the transaction's status as succeeded or failed depending on the status in the notification. At this time, the pending ReleaseActivity objects are deleted.